Colonialism ENDED the genocide that was going on in most of Africa before the Ottoman empire was defeated. A genocide generally referred in older texts as "the islamic slave trade", because islamic economies were entirely dependent on the slave trade for more than a millenium, oh and because it's part of the religion/state that islam was at the time.

Economically it was quite accurate to say that the islamic slave trade WAS islam. As in, everything else was a rounding error. Even now, because the slave trade is still easily 95% of the entire existence of the religion.

For "some" reason people are now trying to rename it "African slave trade". Not at all to get people to focus on the 1% of slaves that went to work in western colonies in the New World (which is what Americans historically called it).